RCA S/PDIF and XLR AES cables have different resistances. I was assured by people more knowledgable than me that that was sub-optimal.
So I got this box finally. The power adaptor doesn't work in the EU, but I was able to get a universal wall wart at a regular all supply store and that worked just fine. Eventually I'll get a better one, like maybe the iFi iPower. I falsely assumed the 9V DC input would accept guitar pedalboard power supply cables, but it didn't. It's a smaller type of plug.
So it works just as advertised. Kemper S/PDIF out goes into the box and an AES cable goes into the Helix AES/EBU input. The Helix picks up the signal fine and everything works as expected. One less AD/DA round in my rig now. Too bad the Helix can't run both S/PDIF and AES at once or I could eliminate one more.
I just realized, since I'm already using my 1/4" main Left output to feed the Kemper, I now have two extra FX loops available in the Helix with this box. That's another reason to shell out the 100 I didn't even consider.

Here ya go!
You should be able to get something out of this quick and dirty patch.
You mentioned Bass - so I have included the basic "Tuck n' Go" (change to whatever suits) in the first slot followed by an Harmonic Flanger at 40% mix, then a Dual Pitch for a slight chorus and finally a legacy Dimension with SW4 on and about 25% mix. Seems like a lot of bother for what the SPX does in one preset. Anyhow kick it around – you may find something in there. Oh, yeah – Zakk Wylde used the SPX90 for those Symphonic tones on No Rest For The Wicked and No More Tears.
PseudoSymphonic.hlx
I read the Yamaha SPX90 Manual, and on Page 13 it states that,
"The programmable parameters for this preset are identical to those for the Stereo Flange preset, omitting the F.B. Gain and MOD DELAY TIME".
Note: Stereo Flange specs a MOD FREQ Range 0.1 ~ 20.0Hz and a MOD DEPTH of 0 ~100%

I've been trying to get a smooth low-pass/high-cut sweep effect, moving from 'very filtered' through to 'no filter', by adding a low pass block and assigning it to the expression pedal. Unfortunately, the parameter seems to move fairly linearly through the frequency range, so almost all the audible effect happens in the first 25% of the parameter's range as the frequency goes from 1KHz up to about 6KHz, and this makes it hard to control a smooth sweep with the foot pedal.
My understanding is that there's no way to change the curve of the expression pedal or the parameter mapping - is that correct?
If so, is there any practical workaround to get a smoother (logarithmic?) sweep between 1Khz and 22KHz/Off??

If you get it opened up and find you don't have a quick FIX for the switch.... AND if you don't use the looper. Just swap the two switches. On my unit the Looper switch is my spare switch... it is never touched so it is essentially new. If one ever dies, I'll just swap it out - LOL
These are just actuators that push the real switch under it.... there shouldn't be any soldering required to swap switches.

Sounds like you started the process backward to me... as already mentioned, and amp sim into an amp (Twin) is not going to yield good results. Plugging into a PA is better (if using the amp sims in the Helix) but if you are new to this, you need to give it time. The Helix is quite capable, your way of thinking will need to change to go the direct route.
You are NOT going to get a tone that sounds like a Twin sitting beside you
You ARE going to get a tone that sounds like a Twin sitting in another room, with a MIC on it, being fed back (and listened to) through your PA system.
If you are a seasoned pro then you will know that there is a big difference between #1 and #2.
As for factory patches.... I'm surprised you are attempting to give them any merit. Presets can give you an idea of how to route a chain, but there are rarely any "real world" tones to work with. Purchased presets are meant to go with studio monitors or FRFR's... it's not fair to judge those when plugged through an amp.
I'm not sure where you did your research, but I don't know of a reputable source that would ever suggest you plug your Helix INTO an amp and attempt to get a good sound from it, especially from factory patches. As for purchased presets, unless the seller told you they were made to go into the front of a Twin, why would you expect it to work?
That would be expected when running an amp. IMO... there is no harm in running the Helix in this manner. If you insert a SEND after the effects you can send that to the AMP then place an AMP sim after that send and send that output to a PA. Voila... you don't have to mic your amp on a stage anymore, but you still get to enjoy it.

Hi all,
I have a XT live which I'm (generally!) happy with, but looking to upgrade. The main problem I have with the XTL is the dirty sounds and amp simulators, I'm not as happy with what I hear as I am with all the mods delays etc. I'm using a FRFR speaker, wondering if upgrading to the 500 (or maybe helix?) is going to give me a vast improvement in these sounds? I mean I obviously know the answer is yes, but can any anyone give me more details?
Cheers!

Well, i had another look at the PC+ to see all the setups i've done and retried the different input.
I've changed between the L6 link and the input 1 and didn't notice any volume difference.
Here are my setups (only on the powercab, the idea is to have the same volume whatever the link you use) ;
_Input1 Gain : 0dB
-Input2 Gain: -10dB (to play lower quickly if i wanted to) I don't use those two inputs now but only the l6link
-Flatlevel : 3dB
- Vintage : -9,5dB
- Green : -9,5dB
- Cream : -10,5dB
- Jarvis : -7,5dB
- Bayou : -10,5dB
- Essex : -8,5dB
- Natural : -9,5dB
I've done this setup if i want to change the speaker model, then, they have the same volume.
The last thing, that wouldn't have any incidence on the sound but i've found it had, i've defined a mic/position/high & low cut for all model speakers : the high and low cuts are at 65/70Hz and 13KHz. The mic is the 160 or 121 Ribbon at 2" or 3" distance.

The question I have is about the PA you used for the Helix. Not all PA's are made equal, and the wattage is really irrelevant. What is relevant is the type of speakers being used on the PA as well as the way you set up your preset. You mentioned it's a powered PA assuming that means you have powered speakers. But there are older generation powered speakers that still rely on simple crossovers and have tone controls, and more modern speakers with DSP driven crossovers and bi-amp designs that have more flat response such as the EV ZLX series, or the Yamaha DXR or DBR series, or the QSC K.2 or CP series and so on. Those will provide the most accurate representation of the elements in your Helix patches because they won't have the typical drop out in the frequency range where the crossover occurs. If you have speakers consistent with those I've mentioned, you really don't need to go through a complete PA to get a feel for the sound from the Helix, you can simply go from the 1/4" L/Mono output to one of the powered speakers. One important aspect when using these type of speakers is to dial in the proper contour adjustments for how they're being used such as Monitor if they're set on the floor to mitigate bass coupling, or default if positioned on a pole and make sure you provide adequate space (around 5 or 6 feet) between you and the speaker in order to not be overwhelmed by the speaker horn.
As mentioned before, it's common to use both high and low cuts to trim out excessive highs and lows on flat response speakers, but that's also highly dependent on the cabinet models, mic models, and mic placements used within your preset. This is nothing new and relates very much to the way these things affect traditional setups. You can achieve a mic mix by selecting a dual cab block and specifying the same speaker on both but with different mics and placements on each. I usually have some form of high and low cuts on my presets, but they tend to be much more subtle due to how I use mic mixes and mic placements on my cabinet models. I normally use a combination of mics such as a MD421 dynamic mic and a R121 ribbon mic typically placed at a distance of around 6 to 8 inches. This mitigates the harsher highs so I rarely have a high cut less than 8 kHz, and more commonly up in the 8.5 to 10 kHz area. My low cuts generally range in the 80 to 125 Hz area. I apply these cuts using a Parametric EQ toward the end of my signal chain. Jason Sadites demonstrates these techniques in his great YouTube series on getting great tone.
One of the things that likely affected your sound when using your Fender Twin (aside from not being able to bypass the preamp and tone stack of the amp through an effect loop input) is the fact you were using a physical guitar cabinet. There are many people that use traditional amps rather the powered flat response speakers normally in some kind of 4CM arrangement, but even in those cases you wouldn't use the Helix cabinets and mics because the Helix cabinets would add additional coloration to the sound of the physical cabinet.

You can't run amp sims into an amp.
If you want to use the Helix amps, you need to run FRFR.
So you say you plugged into the PA?
I'm assuming you mean direct out of the Helix?
Then you need to know about High and low cut filters.
All cabs and IRs (the speaker simulation part of the digital process) need to be EQ'd so the range is similar to a guitar speaker.
There are 2 common ways to do this - use the high and low cut filters on those cabs and IRs - or use global EQ.
The secret is that you don't need to hear much above 5K for a typical guitar sound - even a bright "hifi" clean strat sound.
Distortion hates frequencies above 5k (ish)
So if you want decent overdrives, that's the first thing to do. It also smooths out clean sounds.
Suddenly a Helix amp starts to sound like the thing you know so well.
Next you need to reduce the lows.
Normally somewhere around 100Hz is about the place to roll off the lows.
Those high and low cuts need to be drastic - if you use the global EQ make those curves steep!
Do that, and you will start to get good sounds - direct into a FRFR system.
You can only use the Helix as a pedal board into the front of a guitar amp - you positively don't want to send an amp simulation into an amp!

Mine did too about a year ago after trying it for kicks within 30 minutes. Did a bit searching and found the most likely failure is due to leaking capacitors in the power supply. In fact after opening it up the capacitors leaked in mine. Have not found the time and patience to find replacement parts and try a home repair though ...

The peculiar thing about it all is, when it happened in my case, Helix was the audio card being employed, and the clicks and pops were recorded to the track. Conversely when its an issue of CPU, the artifacts are NOT recorded.

No phantom power, I have also noticed the drop occasionally when using a powered speaker at home rehearsing but at that time the volume would just drop slightly. I only have a few presets made right now that I have memorized, I will do a reset and see if it clears up. My band has progressively been going direct so I thought I would try the helix, if I can’t sort it out I will go back to an amp. When it works it sounds great, when it doesn’t it kills the gig. I normally have a pod pro for a backup but my other guitar player has been using it since I switched to the helix. I’ll put an amp and fx rack back in the trailer going forward.

Thank you, I’m gonna check it out. I only recently became aware that I’m even interested after watching a video with Rick Beato where he was discussing using that preset gently on the distorted bass track to give it a little character and movement.
Since I've also heard it’s great on backing vocals.

Hi guys.
Just to let you know that I've also solved my issue by replacing the USB Controller chip and the USB Port.
This topic was very helpful and I hope all of you can solve your problem as well.
I bought a CY7C68013A-56PVXC (I didn't buy it directly from the Line 6 distributor, I bought it from ebay) and it worked nice.
For those who believe it wouldn't work because it should have a firmware pre instaled, actually it needs a firmware but the firmware isn't located in that part so you don't need to be worried about buying directly on any Line 6 distributors.

Hi shawnt113,
I have an early Yamaha SPX90 in a rack, gathering dust in the corner of my studio! I would probably have to give “it the kiss of life” and spark the thing up to check the settings, and no guarantee of figuring it out, but it maybe worth finding out!
IIRC, it was like some sort of multi voice chorus effect. A big fave of Brian Eno and Daniel Lanois back in the 80s along with that AMS shimmer and Eventide H3000. To get that ensemble sound you could try using a big 70s chorus and the legacy “dimension” to get you in the ball park.
I may investigate further.

Congratulations! By buying a Helix you've stepped boldly into the modern world! By pairing it with a Fender Twin you've succeeded in booting yourself 50 years into the past!
While the Twin is a great amp, it's use with Helix reduces the Helix to a fancy pedalboard. Almost any effect you've ever wanted to put IN FRONT of your tube amp. You don't even have an effects loop!
By using the Helix with your PA you're getting closer to maximizing it's features. You can now use it to create complete rigs - amps, cabs, effects loops, the whole nine yards. Getting it to sound good is, as you've discovered, challenging, especially if your point of reference is one of the world's greatest clean tube amps.
Start by checking out Jason Sadite's YouTube videos. Lots of tips and tricks and he's a great teacher.
However, if that doesn't get you there, and if you can't find a single decent sounding preset, either from the factory or in any of the aftermarket packages, you might want to consider that maybe the modern world isn't for you. Else, maybe you need to sell your Helix and get a Fractal or a KPA.
I don't mean to be insulting or discouraging, but not everybody likes Fords, some prefer Chevies! And a LOT of GREAT music has been made with a Twin and a Tube Screamer!